Apparatus for glass to metal sealing



April 1960 A. D. LA RUE 2,933,855

APPARATUS FOR GLASS TO METAL SEALING Filed Jan. 25. 1956 LAMP IMAGE ADJUSTABLE lND UCTION HEATING UNI T INERT GAS l INVENTOR. ALBERT D. MRl/E ATTORNEYS United States atent APPARATUS FGR GLASS T METAL SEALING Albert 1). La Rue, Lexington, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application January 25, 1956, Serial No. 561,373

17 Claims. (Cl. 49-11) invention relates to the sealing of a glass window in an opening in a Kovar cup as in the fabrication of magnetron output systems where a glass window is sealed across the output iris for the purpose of obtaining a vacuum in the magnetron chamber.

This application is a continuation-in-part of patent application Serial Number 269,478, now abandoned, filed February 1, 1952, for Glass to Metal Sealing Process by Albert D. La Rue.

In the manufacture of electrical devices it is frequently necessary to' provide a window of a dielectric material sealing arr opening in a metallic member. magnetron type' high frequency generator has a metallic casing with an opening for permitting the delivery of output energy. The magnetron casing is hermetically sealed by a window of dielectric material which permits high frequency energy generated by the magnetron to pass therethrough while retaining the vacuum in the magnetron casing. One known method of providing this type of seal is to use glass as the window and to fuse it directly to the metal around the opening by heating the glass to the'fusion point. This is disclosed in US. Patent 2,534,392.

This invention marks a departure from the prior art in that it provides an apparatus for sealing an opening in a metal member, where the transverse dimensions of the opening may be as high as several inches, with a thin flat vitreous window of somewhat larger outside dimensions than the opening without distorting the flat window; where the metal member is cylindrical this is accomplished not only without oxidizing the inside surface of the metallic member during sealing but also with a cleaning up of small amounts of oxide which may be present inside the metal member nearest the region of sealing which is the region of heating.

An object of this invention is to provide a novel apparatus for sealing an opening in a metallic member, with afiat vitreous window Without distorting the window.v

A further object is to provide a novel apparatus for sealing a hollow cylindrical metallic member at one end thereof with a thin flat vitreous window without distorting the window, without oxidizing the inner surface of the metallic member and with a cleaning up small amounts of oxide inside the metallic member nearest the region of the seal.

A further object is to provide a novel apparatus for sealing an opening in a metallic member, where the diameter if round or transverse dimensions of the opening is on the order of several inches, with a thin flat vitreous window of somewhat larger dimensions without distorting the window.

A further object is to provide a novel apparatus for ice tailed description when considered in connection with the accompanying drawing wherein: The single figure shows the apparatus of this invention.

The apparatus of this invention is particularly well suited to sea-ling one end of a cylindrical metallic member, where the inside diameter at that end ranges from about one and one-half to about eight inches in diameter, with a thin flat glass window. A thin flat disk of this glass of a diameter somewhat larger than the inside diameter of the cylindrical metallic member at the one end thereof is placed over that end. A tubular carbon block such as a heating annulus typically of carbon, having an inside diameter at one end thereof to permit the annulus to be slipped over the one end of the metallic member,

Typically; a I

of ninety degrees to virtually preclude any heat radiation from the annulus to the central portion of the thin flat glass disk. An induction heating unit including a coil surrounding at least a part of the annulus provides heating energy to the annulus. The heated annulus in turn heats the peripheral portion of the thin flat glass disk and the contiguous portion of the metallic member by conduction and by radiation. In this way the peripheral portion of the thin flat glass disk is heated to fusion so that the glass disk seals the one end of thecylindrical metallic member. inert gas such as CO wetted with alcohol is introduced under low pressure into the inside of the cylindrical metallic member as the heating commences to flush air out of the inside of the cylindrical metallic member through the end against which the glass disk bears. The inert gas in the cylindrical metallic member prevents oxidation of the inside thereof during sealing. The alcohol aids in cleaning up small amounts of oxide present nearest the region of the seal. Alcohol, a reducing substance carried on a vehicle of inert gas is used instead of a reducing gas such as hydrogen because it is safer by far than the latter. As the glass disk is heated and the peripheral portion fuses, the central portion softens enough to sag. Sagging of the glass disk is prevented by delicately adjusting the pressure of th'einerft gas in the cylindrical metallic member. During'the sealing, the image of a light bulb reflected from the glass window is relied upon for an indication of the convexity or concavity of the glass window. The pressure of the inert gas within the cylindrical metallic member is ad justed to keep the disk planar. The image of an overhead lamp refiected from the glass window has proven to be suitable for this purpose. After fusion is complete at the peripheral portion of the disk, heat input is reduced gradually to prevent cracks or big stresses from developing in the glass window.

With particular reference now to the single figureof the drawing, apparatus is shown for sealing a glass disk 10 of relatively large diameter and having an edge face 10a, over a window opening or a constricted end opening or aperture 12 in a wall of a hollow cylindrical, cup shaped metallic element or member 14. The metallic assesses enclosure 16 shown below member 14 may be a part of a magnetron waveguide arrangement or may be a supporting head upon which is carried out the operation of sealing the glass disk to the member 14. The opposite end 18 of metallic member 14 is forcefully seated in the recessed opening 20 of enclosure 16. Where enclosure 16 as shown or structure equivalent thereto is part of a magnetron waveguide arrangement the member 14 may be afiixed thereto in any suitable manner as with silver solder. A tubular carbon block such as a carbon heating annulus or member 22 is at one end provided with a recess 24 that receives the end portion of member that has the end wall with the window opening 12, whereby the annulus is removably seated over the free or projecting end of the metallic member 14 and fits closely thereon. The inside diameter of the heating annulus intermediate the ends thereof at 26 is barely larger than that of the disk 10 and approximately abuts the peripheral edge face 10a of disk 10 and serves to locate the disk in its proper position coaxial with the opening 12 in member 14. The passage of the heating annulus 22 between the inside diameter 26 and the end face of the annulus that is opposite from the recess 24 is outwardly flared at 28 to define a cone anglewhose spread is on the order of ninety degrees. The flared portion 28 of the heating annulus 22 is an important feature of this invention in order to keep to a minimum the heating of the interior area of the window 10. Because the heat- 1ng annulus 22 is flared at 28, only a very small amount of heat radiated by the heating annulus 22 during a sealing operation reaches and heats the central portion of the flat glass disk 10, because the maximum radiation would be at the inside diameter 26. Disposed around the heating annulus 22 is an induction heating coil 30 which is energized to the extent required by an adjustable induction heating unit 32. The induction heating coil 30 is coupled to the output cables of the adjustable induction heating unit 32 by suitable coupling means 34. When the induction heating unit 32 is on, the heating annulus 22 is inductively heated to raise the temperature pressure control valve 40 is connected by a tube 42 to the bottom of a tank 44 which tank contains a reducing agent such as alcohol. A tube 46 connects the top of the tank 44 to the opening 36 of enclosure 16.

When making a seal, coil 30 is energized by applicallOlhOf high frequency energy thereto by the induction heating unit 32. At the same time that the coil 30 is energized, the valve 40 is opened. Inert gas under some pressure flows from the tank 38, past the pressure control valve 40 through the tube 42, through the alcohol in the tank 44; the alcohol wetted inert gas flows through the tube 46 through the opening 36 of enclosure 16. The alcohol wetted gas flushes the air in the enclosure 16 and member 14 out past the glass disk 10. Flushing out the air prevents oxidation of the interior of member 14 when its temperature is elevated.

As the operation progresses the heating annulus 22 heats up to a high temperature. The member 14 and the peripheral margin or portion 10b of the glass disk 10 are heated by the contiguous portion of the heating annulus 22. The flared portion 28 of the annulus 22 radiates substantially no energy toward the central portion of the glass disk 10. Whereas the peripheral portion of the glass disk is heated to fusion, the central portion of the glass disk 10 is not raised to near as high a tempera ture and only becomes soft enough to sag a little during the process. The sag is ascertained by observation. of the image of an overhead bulb 50 or other convenient light source reflected from the glass disk 19 upon screen 52. The pressure control valve 40 is adjusted till the gas pressure eliminates the sag and the glass disk is held planar. Adjustment of the pressure control valve 40 is guided by observation of the reflected image of the overhead lamp to avoid overadjustment and convexity in the glass disk. During this latter portion of the sealing operation when the temperature is at a maximum the alcohol aids in cleaning up small amounts of oxide which may have been present nearest the region of heat. The energize.- tion of the coil 30 is reduced slowly to permit even cooling.

In accordance with the above-described invention, satisfactory flat glass window seals can readily be made in an opening ranging in outside dimensions from about one and one-half inches to about eight inches. As is conventional, the materials of disk 10 and of member '14 have substantially the same coeflicient of expansion. This invention may be practiced to seal a glass face and metal body of a cathode ray tube.

In certain instances it has been found advantageous to make a graded seal by inserting a thin washer 54 of a material similar to that of disk 10, between the disk 10 and the member 14 before heating begins. Such an insertion improves the thermal properties of the seal when completed. Typically the disk 10 may be made of a glass which is a lithia borosilicate glass. The washer 54 may be of a glass which is a potash borosilicate glass containing a small percentage of alumina. The material employed for member 14 can be of an alloy of the type known as Kovar which is a nickel-cobalt-iron alloy having 28.7 to 29.2% nickel, 17.3 to 17.8% cobalt, 52.9 to 53.4% iron, not more than 0.06% of carbon, not more than 0.5% of manganese, and not more than 0.2% of silicon. Further specifications for Kovar include a coefficient of thermal expansion of 4.33 to 6.2l l()- and a resistivity of approximately 49x10 ohm-centimeters.

The carbon annulus 22 is made of graphite, having a resistivity of approximately .0046 to .0066 ohm/cm.

The heating coil 30 and its disposition are not particularly critical. Typically the coil could be made of one-quarter inch copper pipe having eight to twelve turns with 4; inch to A inch spacing between turns. In disposition the lower four or five turns of the coil would surround the heating annulus with the remaining coil turns above.

It will be observed that with the parts assembled as illustrated in the drawing, the metallic element, or member 14 has an open Window or aperture 12 in an end wall 14a thereof which is disposed approximately horizontal. The shell may be a cup shaped shell, inverted as shown, or of other shape. The recess 24 in the lower or under end face 22a of the annulus or annular heating block or member 22 fits and telescopes over that end of the element or member 14 which has the end wall 14a, and the inner end wall or bottom of the recess abuts and rests upon wall 14a. The inner diameter or passage wall or portion 26 of annular member 22 is larger than the window 12, so as to leave uncovered or exposed, an annular, endless marginal area or zone 14b of the outer or upper face of the end wall 14a, bordering the aperture or window 12. This inner diameter or passage portion 26 of heating member 22 surrounds the peripheral edge or edge face 10a of the glass window or plate 10 which is to be fused to the end wall 14a and confines it in a desired position for fusing on wall 14a centered across the window or aperture 12. The flared wall 28 may be considered as a recess in that portion of that face of the annulus or member 22 which is opposite from that face of the member 22 which abuts wall 14a and borders the opening, window or aperture 12. This flared wall or portion 28 is beveled outwardly and divergently from about the opening or aperture 12, beginning from adjacent to the window. The heating coil or unit 30 constitutesmeans surrounding the annulus or heating element or member 22 for heating it and through it heating said wall 14a and the peripheral margin or portion b of the windowto afusing temperature. Thus the lower end face 22 of heatinglblock 22, through the recess 24, engages and is supported by the end wall 14a of the cup, member or element 14, and the passage 26 of the heating block by engaging the peripheral edge or face 10a of the window 10, positions the window over the aperture 12 of the wall 14a, with a marginal portion 10b of the window 10 overlying or overlapping with the marginal portion 14b of the wall 1 4a that lies along the aperture 12.

While the invention has been described with respect to a glass disk in a similarly shaped opening of a metal member, various modifications can be made in shape and size of theglass window to satisfy any other application of the sealing method and apparatus to electrical devices in which such a window is desired.

'Obviously many modifications and variations of the present invention are possible in the light of the above teachings- It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim: 1. Apparatus for use in sealing a window opening in a metallic wall with a vitreous window where the vitreous window :is slightly larger than the window opening and has a marginal area of a face thereof abutting the marginal face areaof said wall bordering said opening; said;

apparatus comprising a cylindrical tubular carbon'block having transverse dimensions enabling it to seat upon said wall with itspassage wallspaced'from the margin ofsaid opening and surrounding it, the insidetransverse dimen-' sions of the passage of a portion of said carbon block between the ends thereof being only slightly greater than that of the vitreous window whereby said block may closely surround the peripheral edge face of the vitreous window and locate the vitreous window over the window opening, the portion of said block between the portion which fits around the vitreous window and the upper end thereof being flared divergently outwardly and upwardly and means for heating said carbon block to a temperature sufficiently high to heat the peripheral portion of said vitreous window and the contiguous portion of said metallic wall until they effect a seal to one another along their abutting surfaces.

2. Apparatus for use in sealing a glass disk to a flat wall of a metallic member with the disk bridging a window opening in such wall, which comprises a support formed for mounting said member with its said flat wall approximately horizontal, a heating block formed to rest on the top of and be supported stationarily by said flat wall and having a vertical passage therethrough larger horizontally than said window opening and leaving uncovered a marginal area of the upper face of said fiat wall bordering said openig on which the margin of said disk may be supported, said passage having a size and shape horizontally that said block positions said disk to bridge said opening and also overlap with said marginal area of said fiat wall, and means for heating said block, and through said block heating the marginal area of said disk and said marginal area of said flat wall to a temperature at which the margin of the disk fuses to said marginal area of said wall, said block having a wall portion bordering and beginning adjacent the upper end of said passage and which is upwardly divergent, whereby heat radiated from said block above the upper end of said passage will be directed away from the central area of said disk.

3. Apparatus for use in sealing a window opening in the fiat end wall of a cylindrical metallic cup with a flat glass window as defined in claim 2 and further comprising an enclosure having an opening for vertically seating the cylindrical metallic cup by engaging the end of the metallic cup opposite its window end with a fit that is sufficiently close to'substantially preclude flow of gas through the seat of saiden'closure, said enclosure being formed with an inlet, a tank of inert gas under pressure, a control valve on said tank, a tank 'of alcohol, conduit means connected between saidcontrol valve and said alcohol tank and between said alcohol tank and the inlet in said enclosure, whereby upon opening said control valve alcohol-wetted inert gas flows into said enclosure and into said metallic cup.

4. Apparatus for use in sealing a vitreous window across an aperture in a wall of a metallic element, which comprises a support for said element, an annular heating member continuously resting upon and supported by the upper face of said wall'around said aperture and exposing an endless marginal area of said wall bordering said aperture, said member surrounding said marginal area and confining said window in desired position on said wall across said marginal area, said member having a recess in its upper face which leads to said passage and from just above but adjacent said window diverges in an upward direction, and means surrounding said member for inductively heating it, and through it heating said wall and peripheral margin of said window to a fusing temperature. T

5. Apparatus for use in sealing a vitreous window pane to a wall of a metallic element, across an aperture therein, which comprises said element of cup-shape with an aperture in its bottom wall, means for supporting said element in inverted position with its bottom wall uppermost and approximately horizontal, a heating block having a recessed end wall telescoping over and fitting said element and supported stationarily on said element, said block having a vertical passage therethrough aligned with said aperture and of horizontal dimensions slightly larger than said aperture, a vitreous window pane. disposed in said passage, bridging said aperture and confined by said block agaist displacement from bridging position over said aperture, and means surrounding said block for heating it and through it the margin of said window pane and the wall of said element in the area around said aperture to a temperature at which the margin of said pane will fuse to said bottom wall.

6. The apparatus as set forth in claim 5, and means within said supporting means for applying to the under face of said window, during the fusing, a gas under controlled pressure sufficient to prevent material sagging of the central area of the window as that area is softened by the fusing heat along the margins of the window.

7. The apparatus as set forth in claim 5, and means adjacent said Window to reflect heat from said block away from the window and keep to a minimum the heating of the central area of the window.

9. The apparatus as set forth in claim 8, and means I within said supporting means forproviding a temporary support for the central area of the window against material sagging of that central area as it is softened by the fusing heat applied along the margin of the window.

10. The apparatus as set forth in claim 5, and means for replacing the air along the under faces of said wall and window with an inert gas containing a small amount of a reducing gas to prevent oxidation of the wall and to remove any existing oxide from the wall near the region of the seal during the heating.

11. The apparatus as set forth in claimS, and means for replacing the air along the under faces of said wall and window with a reducing gas to remove any existing oxide on the wall near the region of the seal.

7 12. Apparatus for use, in sealing a vitreous window plate to, an end wall ofa shell across an aperture therein, with a marginal area of the plate overlying the margin of said wall bordering said aperture, which comprises means for supporting said shell with said apertured wall approximately horizontal and uppermost, a heating block having a vertical cylindrical passage therethrough and disposed above said support, the dimensions of said pas sage across it being somewhat greater than the corresponding dimensions of said aperture to be bridged by said window plate, whereby when said block rests upon and is supported by said wall the portion of the upper face of that wall bordering said aperture Will be exposed in said passage, said dimensions of said passage being only slightly larger than the corresponding face dimensions of said window plate, so that the passage wall will surround the marginal edge of said window plate and confine it for sealing in proper bridging position across said aperture and against said wall, and means for heating said block and through it the abutting portions of said window plate and said Wall, to a temperature at which said abutting face areas of wall and window plate Iusetogerner.

13. The apparatus as set forth in claim 12, wherein said shell is cup shaped, said supporting means is formed to support the shell in inverted position, and said block has a recess that receives and fits over the top and somewhat down the sides of the shell to locate the block with its passage in desired location relatively to said aperture in the end wall of the shell.

14'. The apparatus as set forth in claim 12 wherein the upper end face of said block beginning adjacent to but above the upper face of said plate is upwardly divergent to reduce to a minimum the heating of the interior area of said plate from said block during the heating for sealing of the marginal strip of said plate.

15. The apparatus as set forth in claim 12, and means for applying a gas under controlled pressure to the interior of the shell during the sealing whereby just enough gas pressure can be exerted beneath the interior area. of said plate to prevent material sagging thereof as it softens under the heating necessary to seal the margin of the plate References Cited in the file of this patent UNITED STATES PATENTS.

1,548,611 Kearsley et al. Aug. 4, 1925 2,015,730 Rosin et al. Oct. 1, 1935, 2,253,054 Tuttle et a1 Aug. 19, 1941 2,432,491 Thomas Dec. 9, 1947 2,480,364 Hansen et al Aug. 30, 1949 2,484,650 Ross, Jr. Oct. 11, 1949 2,499,854 Ellefson Mar. 7', 1950 2,515,706 Greiner et al. July 18, 1950 2,534,392 Walsh Dec. 19, 1950 2,591,666 Barkas et al. Apr. 8, 1952 2,598,286 Mulder et al May 27, 1952 2,629,971 Hare Mar. 3, 1953 2,639,555 Buttino May 26, 1953 2,731,771 Harder, Jr Jan. 24, 1956 2,741,069 Wohlman Apr. 10, 1956 FOREIGN PATENTS 642,444 Great Britain Sept. 6, I950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,933 855 April 26, 1960 Albert D. La Rue It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 12, claim 17 for the claim reference numeral "6" read l6 Signed and sealed this 18th day of October 19609 (SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,933 855 April 26, 1960 Albert D. La Rue It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8 line 12, claim 17, for the claim reference numeral "6" read 16 Signed and sealed this 18th day of October 1960,

(SEAL) Attest:

KARL H. AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

